Properties of Acids and Bases & Theories defining acids and bases

The acids and basesrepresent a large part of human life, Acidsare used in many chemical industries likeFertilizers, Medicines, Plastic & Car batteries, Basesalso have many uses in chemical industries like Soap, Detergents, Dyes & Medicines , For example , The vinegar that is used in some food and cleaning processes is an acidic solution that was early discovered .

Natural and industrial products and the acids and bases entering in their composition or preparation

Properties of Bases

Bases have a bitter taste and slippy feel, Bases change the colour of litmus dye or litmus paper into blue, Bases react with acids producing saltandwater.

Acids and bases

Theories defining acids and bases

The external appearance ofthe acid and baseleads to an experimental definition for each, The experimental definition is based on observation only and doesn’t describe or explain the unseen properties.

The more overall definitions ofacid and base come from the studies and experiments that were placed in the form of theories, Acid-base theories are Arrhenius’s theory , Bronsted- Lowry’s theory and Lewis’s theory.

Na+ (aq) and Cl−(aq) ions are present in both sides of the equation without changing, So, they can be neglected ( cancelled ) from both sides ofthe chemical equation, So, the neutralization reaction can be represented by the following equation :

The Bronsted- Lowry’s theory in 1923

The Danish Scientist Bronsted and the British one Lowry proposed a new acid-base theory , Bronsted-Lowry acid is the substance that give up the proton ( H+ ) , Proton donor , the Bronsted-Lowry base is the substance that accepts the proton ( H+), Proton acceptor .

Application

Bronsted-Lowry theory describes the behaviour of ammonia as a base .

H2 O ( l ) + NH3 ( g )→ NH+4 (aq) + OH– (aq)

When ammonia gas dissolves inthe water, H2 O acts as an acid because it gives up a proton ( H+ ) to ammonia molecule ( NH3 ), As a result of this transfer , OH– formed and it is called Conjugate base , Conjugate base is the substance which is formed when the acid loses a proton ( H+ ) .

NH3 acts as a base because it accepts the proton ( H+ ) from the water molecule , As a result of this transfer, NH+4 formed and it is called Conjugate acid , Conjugate acid is the substance which is formed when the base accepts a proton ( H+ ) .

Lewis’s theory in 1923

Lewis’s proposed an acid-base theory which depends on sharing of a lone pair ofelectronsbetween acidandbase, Lewis acid is the substance that accepts an electron pair or more, Lewis base is the substance that donates an electron pair or more.

Ammonia is considered as a base, although it does not contain hydroxide group in its structure , Because according to Bronsted – Lowry’s theory , Ammonia accepts a proton from another substance ( as water ) during the reaction and according to Lewis’s theory it donates a lone pair of electronsto another substance ( as water ) during the reaction .